This invention relates to the marking or incising of layers, and, more particularly to the precision separation of layers in photovoltaic devices.
In the fabrication of many different kinds of devices it is often necessary to separate the underlying constituents. The separational process can be intricate and difficult in the case of miniaturized devices. In the case of photovoltaic devices such as solar cells there are a number of small scale layers which must be physically parted in order to realize a practical large scale device. In the specific case of amorphous silicon cells the overall structure is formed by three successive layers which must be separated from corresponding layers in adjoining cells. More specifically, a base layer of amorphous silicon overlies a transparent conductive layer, typically of tin oxide, and underlies an outer metallic layer, typically of aluminum.
In order to separate the amorphous silicon layers of adjoining cells, it is common practice to employ a laser beam which is moved along the region that is to be separated. Once the desired separation of the amorphous silicon layers takes place and the overlying layer of aluminum is applied, separation of the aluminum for the adjoining cells can also take place by moving the laser beam along the region intended to be parted.
However, in the case of the outer metallic layer the separation of the metallic portions of adjoining cells is difficult to achieve. This is because there is an alloying reaction that takes place between the semiconductor material such as silicon and most metals when exposed to a high intensity laser beam.
In conventional practice the problem of alloying was countered by the use of masking during the outlying metalization. Unfortunately masking has the effect of significantly reducing the utilization of the active layers of the devices because of the large areas that are required in order to achieve suitable masking. In addition there is invariably a further significant reduction in device area because of difficulties associated with mask misalignment.
In one attempt to overcome the difficulties associated with masking, a photoresist has been employed in which the laser is used to expose the photoresist which is then developed and used in a subsequent etching step. This procedure is objectionable because of the significant cost associated with photoresist chemicals, developers and removers. There is also an undesirable time delay associated with the required separate steps of exposure, development and removal of the photoresist material. There is the further objection that different lasers must be employed for the parting of the base amorphous silicon layer and the overlying conductive layer.
Accordingly, it is an object of the invention to facilitate the marking or incising of layers. A related object is to facilitate the marking or incising of layers employed in photovoltaic devices. Still another related object is to facilitate the marking or incising of the outer metalization layer commonly employed in photovoltaic devices.
Still another object of the invention is to achieve precision separation of layers in photovoltaic devices without requiring the use of different marking and incising apparatuses such as lasers for the various layers. A related object is to permit the marking or incising of layers in photovoltaic devices using common marking apparatus such as a laser for all of the layers in the device.
A further object of the invention is to achieve precision close spacing of adjoing layers in miniaturized devices, particularly in photovoltaic devices formed by an array of miniature solar cells. A related object is to avoid the significant gap between adjoining layers occasioned by the use of masking.
Yet another object of the invention is to avoid the need for photoresist and related procedures in the precision separation of layers in photovoltaic devices. A related object is to avoid the expense, delay and inconvenience associated with the use of photoresist, developers and removers.